Oxalic acid (or ethanedioc acid) [HOOCCOOH] dihydrate is currently manufactured by many different routes. One of the most common routes reacts sodium oxalate with lime (calcium oxide) to precipitate calcium oxalate monohydrate and form an aqueous solution of sodium hydroxide. The calcium oxalate monohydrate is separated from the caustic solution and in another reaction step sulfuric acid is used to precipitate calcium sulfate dihydrate and form an aqueous solution of oxalic acid. This aqueous solution of oxalic acid is separated from the calcium sulfate dihydrate and cooled to induce crystallization of oxalic acid dihydrate. The final filtrate is then typically returned to the sulfuric acid addition step since much of the unused sulfuric acid is still contained in this solution. The calcium sulfate dihydrate forms a solid waste byproduct that often requires landfill disposal.
Oxalic acid or its dihydrate is used currently in the following commercial applications: in textile finishing as a bleach or stain remover, as a metal cleaning agent, as wood bleach or wood stain lightener and in the tanning and finishing of leather. It is also used as an additive to increase fertilizers and in artillery ammunition to suppress flashing. These relatively limited commercial uses have not spurred a commercial demand for finding a more efficient method for oxalic acid manufacture; and production by the current manufacture methods has kept pace with the modest worldwide demand for the acid.
Specifically needed to improve the efficiency of oxalic acid dihydrate production is a process made in one reaction chamber, i.e., a one-pot process, and one that is more environmentally benign, such as when the discharge waste salt of such a process is sodium chloride, which need not be disposed in a landfill.